Synergized hemiacetals composition and method for scavenging sulfides and mercaptans

ABSTRACT

This invention provides a composition comprising
         I. at least one reaction product between a nitrogen-free monohydric alcohol and an aldehyde or ketone, and   II. at least one reaction product between a nitrogen-free sugar alcohol and an aldehyde or ketone, and optionally   III. at least one reaction product from   III.a) formaldehyde, and   III.b) an amine, selected from the group consisting of primary alkyl amines having 1 to 4 carbon atoms, and primary hydroxy alkyl amines having 2 to 4 carbon atoms, and optionally   IV. at least one solid suppression agent selected from the group consisting of   IV(a). alkali or alkaline earth metal hydroxides   IV(b). mono-, di- or tri-hydroxy alkyl, aryl or alkylaryl amines,   IV(c). mono-, di- or tri-alkyl, aryl or alkylaryl primary, secondary and tertiary amines or   IV(d). multifunctional amines and   IV(e). mixtures of compounds of groups IV(a) to IV(c).   wherein alkyl is C 1  to C 15 , aryl is C 6  to C 15  and alkylaryl is C 7  to C 15 .

The invention relates to a composition and a process for scavenginghydrogen sulfide from liquids and/or gas by using a synergisticcombination of acetals in admixture with a reaction product fromformaldehyde and amines and/or a solids suppression agent. Theformulations containing the inventive composition have particularapplicability in scavenging hydrogen sulfide and/or mercaptans yet atthe same time prevent the formation of unwanted emulsions and/ordeposition of unwanted by-products often associated with usingchemistries and/or formulations of the prior art.

The presence of compounds containing a sulfhydryl group (—SH) andparticularly of hydrogen sulfide pose challenges in many industries.Their presence can create a significant health, safety and environmentalchallenge. There are many different types of compounds containing asulfhydryl group (“sulfhydryl compounds”), with the most commonlyencountered molecules including hydrogen sulfide (H₂S), organo-sulfurcompounds containing R—SH groups (also called mercaptans),thiocarboxylic acids RC(O)SH, dithiocarboxylic acids RC(S)SH, andrelated compounds.

In the oil and gas industry the H₂S content of crude oil and natural gasin many areas of the world is high enough to present environmental andsafety hazards. Hydrogen sulfide is a flammable, corrosive, and highlytoxic gas. H₂S is the most reduced form of sulfur and is produced bysulfate reducing bacteria (SRB) that are often found in anaerobicoilfield environments, or caused by thermal cracking and thermochemicalsulfate reduction (TSR) by hydrocarbons. As crude oil is produced, it isdepressurized and dissolved H₂S is released and can then be transferredto, for example, oil based drilling fluid during the drilling processand this can become a hazard as the drilling fluid is recirculated fromthe well to the surface. During the production phase of crude oil andnatural gas H₂S gas can create a significant asset integrity risk as itis an acid gas and upon dissolving into produced water creates a verycorrosive environment. In addition, the presence of H₂S increases therisks of sulfide stress cracking, hydrogen embrittlement and pittingcorrosion of some structural materials and requires to be removed inorder for fluids and gases to be safely processed.

The odor of sulfhydryl compounds is also a challenge in, for example,metal working environments, but equally in water treatment processes,either municipal (e.g. waste water treatment) or industrial (e.g.recycling of mining water). SRB are often present in the recirculatingfluid systems, and though the bacteria can usually be controlled by theuse of biocidal compositions, often control of the biology in the systemgets lost which results in the development of hazardous H₂S and/ormercaptans in the system. Furthermore biocides are inefficient atremoving H₂S after it forms and only anecdotally scavenge H₂S, viaeither oxidation (e.g. sodium hypochlorite application) or due to therelease of low levels of aldehyde during their breakdown (e.g. withglutaraldehyde). Sulfhydryl compounds and particularly H₂S can presentenvironmental, toxicity and integrity challenges in gaseous phases inconfined spaces, as for instance in sewage treatment facilities andparticularly in shipping and storage containers for moisture sensitivematerials that may emit H₂S which can accumulate in the gaseousheadspace. It would be desirable to have a scavenger that can reduce theH₂S concentration in such locations.

Most commonly used sulfhydryl scavengers are based on metals as forexample copper, zinc or iron which are converted to insoluble sulfides.A number of alternative, metal free methods have been proposed toscavenge hydrogen sulfide and to control sulfhydryl odors in hydrocarboncontaining systems, including:

WO-98/02501 describes the use of bisoxazolidines prepared by thereaction of 1,2- or 1,3-amino alcohols containing 3 to 7 carbon atomswith aldehydes containing 4 or fewer carbon atoms, as for example3,3′-methylenebis-5-methyloxazolidine. The relative oil and watersolubility of these products can be controlled through the choice ofstarting materials. These bisoxazolidines react with sulfhydrylcompounds present in oil and gas streams to neutralize and thereforescavenge them.

U.S. Pat. No. 5,347,004 teaches the use of reaction products ofalkoxyalkylene amine, optionally in admixture with ammonia and/oralkylamines with aldehydes to remove H₂S from gas streams which aresparged into water solutions of the reaction products.

WO-2014/031537 teaches the use of an aldehyde releasing compound,preferably a hydantoin compound, to remove sulfhydryl compounds fromhydrocarbon fluids.

U.S. Pat. No. 3,928,211 describes the use of inorganic zinc salts (mostpreferably zinc carbonate) preferably dispersed in aqueous ornon-aqueous oil well drilling fluids with an organic dispersant such aslignin containing materials for scavenging hydrogen sulfide in aqueousdrilling fluids.

WO-2002/051968 teaches a process for reducing the level of hydrogensulfide in a liquid or gas by treatment of the liquid or gas with anH₂S-scavenger product derivable from the reaction of a carbonylgroup-containing compound with an alcohol, thiol, amide, thioamide, ureaor thiourea. The carbonyl group-containing compound is preferablyformaldehyde, and preferably the product is derivable by reaction offormaldehyde with an amine-free alcohol or urea selected from ethyleneglycol, propylene glycol, glycerol, diethylene glycol, triethyleneglycol, ethyl alcohol, n-butanol, a sugar, a low molecular weightpolyvinyl alcohol, castor oil fatty acid and urea. More especially, thescavenger product is used with an amine, especially monoethanolamine ormonoethanolamine triazine.

U.S. Pat. No. 4,978,512 teaches a method of reducing H₂S levels, themethod comprising bringing the H₂S containing medium into contact withinter alia acetals and bisoxazolidines.

The object of this invention is to provide compositions which can beused for scavenging of sulfhydryl compounds in crude oil, gasproduction, water production, water injection and combinations thereof,preferably, but not limited to H₂S and/or mercaptans. The compositionsof the invention should be notable for improved safety and performancecompared to the formulations and chemistries of the prior art, i.e. theyshould contain low amounts of toxic substances like free formaldehydeeven after prolonged storage. They should have a higher scavengingefficiency than scavengers according to the state of the art andespecially for the treatment of gases as for example of natural gas theyshould assure an efficient scavenging of sulfhydryl compounds within ashort contact time. Furthermore it is desirable to have a scavenger thatdoes not produce unwanted solid by-products and/or form emulsions thatcan inadvertently contaminate the very systems they are treating. Inparticular the formation of solid products which may plug lines andvessels shall be retarded or even inhibited in order to facilitate theremoval of the sulfhydryl reaction products formed during the scavengingprocess.

Surprisingly it has been found that a composition comprising at leastone reaction product between a monohydric alcohol and an aldehyde orketone and at least one reaction product of a sugar alcohol and analdehyde or ketone shows improved capability in scavenging sulfhydrylcompounds in comparison to the respective reaction products of theindividual alcohols. Such composition allows i) for a lower dosage rateof scavenger to obtain the same level of residual amount of sulfhydrylcompound and/or ii) for a lower level of residual amount of sulfhydrylcompound with the same dosage rate of scavenger. Furthermore, incombination with at least one reaction product from formaldehyde and anamine (hereinafter also referred to as “synergist”) the kinetics ofscavenging H₂S and/or mercaptans provided by the reaction products of amonohydric alcohol and a sugar alcohol with an aldehyde and/or ketonecan be significantly accelerated. Alternatively to the synergist or inaddition to the synergist, the admixture of a solids suppression agentas a further synergistic additive facilitates the removal of sulfhydrylreaction products especially in continuously operated scavengingprocesses. Furthermore the admixture of the synergist and/or the furthersynergist extends the gas breakthrough time of sulfhydryl compounds in acontact tower containing the reaction products of a monohydric alcoholwith an aldehyde and/or ketone and a sugar alcohol with an aldehydeand/or ketone.

The use of the synergist and/or the further synergist of the inventionenables the mixed hemiacetals and acetals to react much more efficientlywith sulfhydryl compounds and especially with H₂S. The mechanismbelieved to be involved in this reaction, but which should not beconsidered to be limiting to the invention in any way, occurs due to thelikelihood that the synergist component reacts preferentially with H₂Sforming an intermediate reaction complex which then in turn reacts witha molecule of hemiacetal respectively acetal reforming a molecule ofsynergist and liberation of the corresponding alcohol present in the(hemi-)acetal. After the H₂S scavenging process the residual synergistthen works as a corrosion inhibitor, protecting the integrity of thepipelines and equipment in which it has been applied.

Within the scope of this application the expressions “hemiacetal” and“acetal” encompass the reaction products of an alcohol with either analdehyde or a ketone, i. e. they include hemiketals respectively ketalswhen using a ketone instead of an aldehyde in the reaction with anmonohydric and/or sugar alcohol. The expression “(hemi-)acetals”encompasses hemiacetals, acetals and their mixtures which are oftenformed during reaction of alcohols and carbonyl compounds.

In a first aspect of the invention, there is provided a compositioncomprising

-   -   I. at least one reaction product between a nitrogen-free        monohydric alcohol and an aldehyde or ketone, and    -   II. at least one reaction product between a sugar alcohol and an        aldehyde or ketone.

In a second aspect of the invention there is provided a compositioncomprising

-   -   I. at least one reaction product between a nitrogen-free        monohydric alcohol and an aldehyde or ketone, and    -   II. at least one reaction product between a sugar alcohol and an        aldehyde or ketone, and    -   III. at least one reaction product from formaldehyde and ammonia        and/or an amine selected from the group consisting of primary        alkyl amines having 1 to 10 carbon atoms and primary hydroxy        alkyl amines having 2 to 10 carbon atoms.

In a third aspect of the invention there is provided a compositioncomprising

-   -   I. at least one reaction product between a nitrogen-free        monohydric alcohol and an aldehyde or ketone, and    -   II. at least one reaction product between a sugar alcohol and an        aldehyde or ketone, and    -   IV. at least one inorganic or organic alkaline compound that        functions as a solids suppression agent.

In a fourth aspect of the invention there is provided a compositioncomprising

-   -   I. at least one reaction product between a nitrogen-free        monohydric alcohol and an aldehyde or ketone, and    -   II. at least one reaction product between a sugar alcohol and an        aldehyde or ketone, and    -   III. at least one reaction product from formaldehyde and ammonia        and/or an amine selected from the group consisting of primary        alkyl amines having 1 to 10 carbon atoms and primary hydroxy        alkyl amines having 2 to 10 carbon atoms, and    -   IV. at least one inorganic or organic alkaline compound that        functions as a solids suppression agent.

In a fifth aspect of the invention, there is provided the use of thecomposition of the first, second, third or fourth aspect of theinvention as a scavenger for sulfhydryl compounds for application inoilfield operations and process systems.

In a sixth aspect of the invention, there is provided a process forscavenging sulfhydryl compounds in oilfield operations and processsystems, the process comprising adding to a system susceptible toliberation of sulfhydryl compounds the composition of the first, second,third or fourth aspect of the invention.

In a seventh aspect of the invention there is provided the use of atleast one reaction product from

-   -   III. formaldehyde and ammonia and/or an amine, selected from the        group consisting of primary alkyl amines having 1 to 10 carbon        atoms and primary hydroxy alkyl amines having 2 to 10 carbon        atoms,

as a synergist in the reaction between

-   -   a) I. the reaction product between a nitrogen-free monohydric        alcohol and an aldehyde or ketone, and    -   a) II. the reaction product between a sugar alcohol and an        aldehyde or ketone, and    -   b) a sulfhydryl compound.

In an eighth aspect of the invention there is provided the use of atleast

-   -   IV. one inorganic or organic alkaline compound

as a solids suppression agent in the reaction between

-   -   a) I. the reaction product between a nitrogen-free monohydric        alcohol and an aldehyde or ketone, and    -   a) II. the reaction product between a sugar alcohol and an        aldehyde or ketone, and    -   b) a sulfhydryl compound.

In preferred embodiments of the invention, at least one demulsifier (V)and/or corrosion inhibitor (VI) is present in any aspect of theinvention.

Group I

The group I compound is the reaction product of a monohydric alcohol andan aldehyde or ketone. The monohydric alcohol does not contain nitrogen.

Preferred monohydric alcohols as starting materials are alkyl, aryl andarylalkyl alcohols containing one hydroxy group and 1 to 15 carbonatoms, more preferably 1 to 10 carbon atoms and especially 2 to 5 carbonatoms as for example 1 to 5, or 2 to 15, or 2 to 10 carbon atoms. Thehydroxyl group of preferred monohydric alcohols is bound to analiphatic, alicyclic and/or aromatic moiety, preferably to an aliphatic,alicyclic and/or aromatic hydrocarbon moiety, and more especially to analiphatic or cycloaliphatic hydrocarbon moiety. The aliphatic andcycloaliphatic moieties may be saturated or unsaturated, preferably theyare saturated. Aliphatic moieties with 3 or more carbon atoms may belinear or branched. More especially the monohydric alcohol is aliphatic.In particular the alcohol is an alkyl alcohol. Examples for preferredalcohols are methanol, ethanol, propanol, iso-propanol, n-butanol,iso-butanol, tert-butanol and the various isomers of pentanol, hexanol,heptanol and octanol as for example 2-ethyl hexanol and their mixtures.Especially preferred are methanol and ethanol.

Preferred aldehydes or ketones as starting materials contain one or morecarbonyl groups, more preferably one or two carbonyl groups andespecially one carbonyl group. Furthermore, preferred aldehydes andketones contain 1 to 10 carbon atoms, more preferably 1 to 7, andespecially 1 to 4 carbon atoms. In preferred aldehydes the carbonylgroup carries one and in preferred ketones two aliphatic, alicyclicand/or aromatic substituents. More preferably the substituents arealiphatic, alicyclic and/or aromatic hydrocarbon substituents andespecially the substituents are aliphatic hydrocarbon groups. Preferredaliphatic and cycloaliphatic substituents may be saturated orunsaturated, most preferably they are saturated. In a particularlypreferred embodiment the saturated aliphatic groups are alkyl groups. Inketones both substituents may be the same or different.

In a preferred embodiment the carbonyl compound is an aldehyde, morepreferably a mono- or di-aldehyde, and especially formaldehyde. Itshould be understood that the terms “aldehyde” and “formaldehyde”include precursors like e.g. para-formaldehyde, formalin, and otherchemical forms from which the basic structure HCHO can be released orset free during the reaction with an alcohol. Other suitable aldehydesinclude, for example, acetaldehyde, propionaldehyde, butyraldehyde,glutaraldehyde and glyoxal. Suitable ketones include, for example,acetone, methyl ethyl ketone, diethylketone, methyl isopropyl ketone,hexanones and heptanones.

Mixtures of two or more carbonyl compounds, for example two or more ofthe aldehydes mentioned above, e.g. formaldehyde and one or more otheraldehydes, may be used if desired.

In the reaction between monohydric alcohol and aldehyde and/or ketonepart or all of the alcohols may be converted to hemiacetals and/oracetals. In a preferred embodiment, the reaction product is ahemiacetal. In a preferred embodiment at least 50 mol-% of the alcohol,more preferably 60 to 99 mol-% of the alcohol, especially 65 to 95 mol-%of the alcohol and especially preferred 70 to 90 mol-% of the alcohol asfor example more than 60 mol-%, more than 65 mol-%, more than 70 mol-%,% of the alcohol or 50 to 99 mol-%, 50 to 95 mol-%, 50 to 90 mol-%, 60to 95%, 60 to 90 mol-%, 65 to 99 mol-%, 65 to 90 mol-%, 70 to 99 mol-%or 70 to 95 mol-% of the alcohol are converted to hemiacetals and/oracetals. In case the degree of conversion is low, some unreactedmonohydric alcohol remains in the composition. The presence of residualalcohol in the reaction mixture has proven to be advantageous as uponits reaction with sulfhydryl compounds often the formation of solidprecipitate gets reduced. Furthermore, remaining alcohol will act as asolvent.

Group II

The group II compound is the reaction product of a sugar alcohol and analdehyde or ketone. Sugar alcohols are also known as “alditols”.

Preferred sugar alcohols as starting materials for the group IIcompounds are polyols obtainable by reduction of the carbonyl group ofsaccharides whereby an aldehyde or ketone function is replaced by ahydroxyl group. Accordingly sugar alcohols differ from carbohydrates inthat they lack a carbonyl group. Preferred sugar alcohols arenon-reducing. Preferably the sugar alcohol does not contain nitrogen. Areview on sugar alcohols has been published in 2012 by H. Schiweck etal. in Ullmann's Encyclopedia of Industrial Chemistry.

Preferred sugar alcohols have 4 to 12 carbon atoms and 4 to 10 hydroxylgroups, more preferably 4 to 6 carbon atoms and 4 to 6 hydroxyl groupsand especially 5 or 6 carbon atoms and 5 or 6 hydroxyl groups whereinnot more than one hydroxyl group is bound to each carbon atom.

In preferred sugar alcohols with 4 to 6 carbon atoms each carbon atomcarries one hydroxyl group. The carbon chain is preferably saturated andmay be linear (“glykitols”) or cyclic (“cyclitols”). According to theirstereochemistry different isomers exist. All isomers are similarlysuited as starting material for the group II compound.

Preferred linear sugar alcohols have the general formula (1)

HO—CH₂—(CHOH)_(n)—CH₂—OH   (1)

wherein n is an integer between 2 and 4 as for example 2, 3 or 4.

Preferred sugar alcohols with 4 carbon atoms and 4 hydroxy groups(“tetritols”) are erythritol and threitol. Preferred sugar alcohols with5 carbon atoms and 5 hydroxy groups (“pentitols”) are arabitol, ribitoland xylitol. Preferred sugar alcohols with 6 carbon atoms and 6 hydroxygroups (“hexitols”) are allitol, galactitol (=dulcitol), glucitol(=sorbitol), iditol, mannitol and talitol (=altritol).

Preferred cyclic sugar alcohols have the molecular formula C₆H₆(OH)₆.Most preferred cyclic sugar alcohols are the various stereoisomers of1,2,3,4,5,6-cylcohexanehexol (inositol). Especially preferred cyclicsugar alcohol is cis-1,2,3,5-trans-4,6-cyclohexanehexol(“myo-inositol”).

The majority of sugar alcohols occur naturally in the vegetable kingdom.Accordingly they can be extracted from plant raw material or marinealgae. Most of the sugar alcohols can also be produced synthetically,for example by catalytic hydrogenation of sugars and/or by fermentativeor enzymatic processes starting from simple sugars and especially frommonoglycerides like xylose, glucose, sucrose and mannose. Linearhexitols with the general formula HO—CH₂—(CHOH)₄—CH₂—OH can be producedfrom the structurally related hexoses by catalytic reduction. Forexample, sorbitol and mannitol are obtained in technical quantities byhydrogenation of glucose and mannose using Raney nickel catalysts.Erythritol on the other hand is obtained predominantly by fermentationof glucose or sucrose.

In a further preferred embodiment more complex disaccharide sugaralcohols obtained by reduction of disaccharides are used as startingmaterials for the group II compound. Preferred disaccharide sugaralcohols contain a saccharide moiety bound to a linear sugar alcoholmoiety via an acetal or ketal link. Examples for sugar alcoholscontaining a saccharide moiety are the isomalt diastereomers(6-O-α-D-glucopyranosyl-D-sorbitol and1-O-α-D-glucopyranosyl-D-mannitol), the maltitol isomers(4-O-α-D-glucopyranosyl-D-sorbitol and4-O-α-D-glucopyranosyl-D-glucitol) and lactitol(4-O-(β-D-galactopyranosyl)-D-glucitol).

In a further preferred embodiment partial esters and ethers of sugaralcohols are used as starting materials for the group II compound.Preferred partial esters and ethers contain at least two, preferably atleast three and more preferably at least four as for example 5non-derivatised hydroxyl groups which are accessible for reaction withan aldehyde or ketone. Especially preferred are esters with C₁- toC₂₄-carboxylic acids and ethers with C₁- to C₂₄-alcohols and ethersformed by intramolecular dehydration reaction. Examples for suitedderivatives of sugar alcohols are pinitol((1S,2S,4S,5R)-6-methoxycyclohexane-1,2,3,4,5-pentol), 1,4-sorbitan,3,6-sorbitan and isosorbide.

The most preferred sugar alcohols used as starting materials for thegroup II compound are sorbitol, xylitol, erythritol, mannitol, lactitol,isomalt and maltitol.

For the reaction between sugar alcohol and aldehyde and/or ketone thesugar alcohol may be applied as a solid or as a concentrated solutionoften called syrup.

Preferred aldehydes and ketones as starting materials for the group IIcompounds are the aldehydes and ketones that have already been describedabove with respect to group I. Most preferred aldehyde as startingmaterial for group II compounds is formaldehyde. The aldehyde or ketoneused for reaction with the sugar alcohol may be the same as the one usedfor the monohydric alcohol, or it may be a different one.

In the reaction between sugar alcohol and aldehyde and/or ketone part orall of the hydroxyl groups may be converted to hemiacetals and/oracetals. In a preferred embodiment at least 50 mol-% of the hydroxylgroups, more preferably 60 to 99 mol-% of the hydroxyl groups,especially 65 to 95 mol-% of the hydroxyl groups and especiallypreferred 70 to 90 mol-% of the hydroxyl groups as for example more than60 mol-%, more than 65 mol-%, more than 70 mol-%, or 50 to 99 mol-%, 50to 95 mol-%, 50 to 90 mol-%, 60 to 95%, 60 to 90 mol-%, 65 to 99 mol-%,65 to 90 mol-%, 70 to 99 mol-% or 70 to 95 mol-% of the hydroxyl groupsare converted to hemiacetals and/or acetals. In case the degree ofconversion is low some unreacted sugar alcohol remains in thecomposition. The presence of residual hydroxyl groups in the reactionmixture has proven to be advantageous as upon its reaction withsulfhydryl compounds the formation of solid precipitate gets reduced.

In a particularly preferred embodiment the reaction product between thesugar alcohol respectively the monohydric alcohol and the aldehyde ispredominantly a mixture of hemiacetals and acetals. Preferred arereaction products wherein the ratio between hemiacetals and acetals on amolar basis is between 100:1 and 1:10 more preferably between 50:1 and1:5 and especially between 20:1 and 1:1 as for example between 100:1 and1:5 or between 100:1 and 1:1 or between 50:1 and 1:10 or between 50:1and 1:1 or between 20:1 and 1:10 or between 20:1 and 1:5.

Preferred polyhydric hemiacetal compounds derived from sugar alcoholsthat can be used as the scavenger are exemplified by the structures (2)to (5) derived from glucitol below:

wherein

R₁ is H or C₁ to C₉ alkyl.

The corresponding enantiomers and diastereomers based on other sugaralcohols are similarly suited.

Reactions of aldehydes and ketones with alcohols are described in theliterature. “Formaldehyde”, p 265, Joseph Frederic Walker, reprint 1975,Robert E. Krieger Publishing Company Inc. discloses that hemiacetals areobtained when formaldehyde and alcohols are brought together underneutral or alkaline conditions, and that they form readily in the caseof primary and secondary alcohols.

The synthesis of compounds of group I and group II may be accomplishedin separate reactions. Preferably it is accomplished in a simultaneousreaction using a one pot reaction by charging a mixture of monohydricalcohol and sugar alcohol and reacting this mixture with the aldehydeand/or ketone. A one-pot reaction is especially preferred when thealdehyde used for the reaction with the monohydric alcohol is the sameas the aldehyde used for the reaction with the sugar alcohol.

For ease of reaction the presence of an aqueous solvent has proven to beadvantageous. Preferably the reaction is made in the presence of 5 to 70wt.-%, more preferably in the presence of 10 to 50 wt.-% and especiallyin the presence of 15 to 40 wt.-% of water in respect to the overallreaction mass. Often the amount of water introduced by the reactantslike for example by formalin is sufficient. In a preferred embodimentthe water remains in the reaction product.

In the synthesis of compounds of group I and group II the molar ratio ofhydroxyl groups to carbonyl groups is preferably between 20:1 and 1:5and more preferably between 10:1 and 1:2 and especially between 2:1 and1:1 as for example between 20:1 and 1:2 or between 20:1 and 1:1 orbetween 10:1 and 1:5 or between 10:1 and 1:1 or between 2:1 and 1:5 orbetween 2:1 and 1:2. In a preferred embodiment the reactants are reactedin a substantially stoichiometric ratio.

However, in order to reduce the presence of residual (unreacted) freecarbonyl compound in the final product to extremely low levels it hasproven to be advantageous not to proceed to full reaction of allhydroxyl groups, i.e. to react only part of the hydroxy groups of thealcohols of groups I and/or II with the aldehyde. Accordingly, in apreferred embodiment the reaction between the alcohols and the aldehydeis made with less than the stoichiometric amount of carbonyl compound inrespect to the hydroxyl groups of the alcohols. A preferred molar ratioof carbonyl groups to hydroxyl groups is between 1.01:1.50 andespecially between 1.05 and 1.20 as for example between 1.01 and 1.20 orbetween 1.05 and 1.50. The ratios given above similarly apply for thereaction of the carbonyl compound with the monohydric alcohols of groupI respectively with the sugar alcohols of group II in separate reactionsteps as well as for the reaction with their mixture in a one-potreaction.

Group III

The group III component is optional. The group III compound is thereaction product from formaldehyde with ammonia and/or an amine, theamine being selected from the group consisting of primary alkyl amineshaving 1 to 10 carbon atoms and primary hydroxy alkyl amines having 2 to10 carbon atoms. This group comprises the synergist component of theinventive composition according to the second and fourth aspect of theinvention.

Preferred primary amines comprise 1 to 4 carbon atoms, preferred primaryhydroxy amines 2 to 4 carbon atoms. Especially preferred primary hydroxyamines correspond to the formula (6)

HO-A-NH₂   (6)

wherein A is a linear or branched alkylene group with 2 to 4 carbonatoms.

Examples of nitrogen containing compounds suitable for the presentinvention include, but are not limited to: ammonia, methylamine,ethylamine, propylamine, isopropyl amine, monoethanolamine,1-amino-2-propanol, 3-amino-1-propanol, 2-amino-1-butanol,3-amino-1-butanol, 3-amino-1-butanol, 2-ethoxypropylamine,3-ethoxypropylamine, 1-methoxyisopropylamine and 2-methoxyethylamine.

The nitrogen containing compound and formaldehyde may be reacted in anymolar ratio with a preferred ratio being from 1 mole aldehyde to 10moles nitrogen containing compound to 10 moles aldehyde to 1 molenitrogen containing compound, a more preferred ratio being from 1 molealdehyde to 5 moles nitrogen containing compound to 5 moles aldehyde to1 mole nitrogen containing compound, an even more preferred ratio being1 mole aldehyde to 3 moles nitrogen containing compound to 3 molesaldehyde to 1 mole nitrogen containing compound and a most preferredratio being 1 mole aldehyde to 1 mole nitrogen containing compound.

The structure of the aminal formed from the reaction of formaldehyde andthe nitrogen containing compound is dependent upon the selected nitrogencontaining compound and the selected molar ratio between formaldehydeand nitrogen compound, as is self-evident to those of ordinary skill inthe art. Similarly, mixtures of the above nitrogen containing compoundsmay also be reacted in order to form singular, or mixtures of variousaminals as is also evident to one of ordinary skill in the art.

In one preferred embodiment the reaction product corresponds to formula(6a)

wherein

R is H or methyl, and

n is 1 or 2.

In an especially preferred embodiment R is CH₃. In another especiallypreferred embodiment, n is 1. In a particularly preferred embodiment nis 1 and R is CH₃. The name of this compound is3,3′-methylenebis-5-methyl-oxazolidine (MBO).

In another preferred embodiment the reaction product corresponds toformula (6b)

wherein each R² is C₁ to C₄ alkyl or C₂ to C₄ hydroxy alkyl. Examplesfor especially preferred compounds arehexahydro-1,3,5-trimethyl-s-triazine,hexahydro-1,3,5-triethyl-s-triazine,hexahydro-1,3,5-tris(hydroxymethyl)-s-triazine andhexahydro-1,3,5-tris(2-hydroxyethyl)-s-triazine.

Mixtures of different reaction products of structures 6a and 6b areequally suited. The substituents R and R² may be the same or different.

Group IV

The group IV component is optional. The group IV compound is aninorganic or organic alkaline compound. This group comprises the solidssuppression agent of the inventive composition according to the thirdand fourth aspect of the invention.

The solid usually formed by the reaction of group I and group IIcompounds with hydrogen sulfide is 1,3,5-trithiane. Addition of analkaline compound to the compounds of groups I and II prevents or atleast retards the formation of the poorly soluble 1,3,5-trithiane upontheir reaction with sulfhydryl compounds. Without being bound to thistheory it is believed that different intermediates as for examplepolyoxymethylenesulfide oligomers are formed and stabilized by thepresence of the alkaline compound of group IV. By preventing theformation of solids the scavenging composition remains homogeneous andespecially in a contact tower application allows for more efficient andup to quantitative use of the (hemi-)acetals of group I and II compoundsand thereby reduces the amount of chemicals required. This may result inan extended gas breakthrough time in such scavenging applications.Additionally, in direct injection applications for continuous scavengingof sulfhydryl compounds from e.g. natural gas streams the removal of theliquid reaction products is much easier than removal of solids and it isnot prone to blockage of tubings and vessels.

Furthermore, in the presence of an alkaline compound of group IV thestability of compounds I and II is increased and e.g. gassing offormaldehyde is further reduced or even prevented. This leads to afurther reduced level of free formaldehyde in the space above thecomposition and thereby further improves the safety of the personnelhandling the inventive composition.

Preferably, the compound of group IV is soluble in, or miscible with themixture of compounds of groups I and II. In a further preferredembodiment the compound of group IV is soluble in, or miscible with theformulation of the mixture of compounds of groups I and II in thepresence of an aqueous solvent.

In a preferred embodiment, the alkaline compound is selected from thegroup consisting of

IV(a). alkaline metal salts or alkaline earth metal salts,

IV(b). ammonia; alkyl amines, aryl amines or alkylaryl amines,

IV(c). hydroxy alkyl amines, hydroxy aryl amines or hydroxy alkylarylamines,

IV(d). multifunctional amines, and

IV(e). mixtures of compounds of groups IV(a) to IV(c).

In an aryl amine, the N atom is bonded to the aromatic system. In analkyl aryl amine, the N atom may be bonded to either the aromatic systemor the alkyl group.

Preferred cations of the alkaline metal and alkaline earth metal saltsIV(a) are derived from lithium, sodium, potassium, rubidium, beryllium,magnesium, calcium and strontium with sodium, potassium and calciumbeing especially preferred. Preferred anions are hydroxyl and carbonategroups with hydroxyl being especially preferred. Examples for preferredalkali or alkaline earth metal salts LiOH, NaOH, KOH, Mg(OH)₂, Ca(OH)₂,Be(OH)₂, Na₂CO₃, K₂CO₃, NaHCO₃, KHCO₃, BeCO₃, MgCO₃, CaCO₃, Mg(HCO₃)₂,Ca(HCO₃)₂ and their mixtures. Especially preferred alkali and alkalineearth metal salts of group IVa are NaOH, KOH, Mg(OH)₂ and Ca(OH)₂.

The amines of group IV(b) may be primary, secondary or tertiary amines.Preferred amines have up to 20 carbon atoms, more preferably between 1and 10 and especially between 2 and 4 carbon atoms as for examplebetween 1 and 20, between 1 and 4, between 2 and 20 or between 2 and 10carbon atoms. Preferred hydrocarbyl residues are alkyl, aryl andalkylaryl residues, with alkyl residues being particularly preferred. Insecondary and tertiary amines the hydrocarbyl residues may be the sameor different. Especially preferred amines are alkyl amines with 1 to 4carbon atoms per alkyl residue. Examples for especially preferred aminesare methylamine, dimethylamine, trimethylamine, ethylamine,diethylamine, triethylamine, propylamine, isopropylamine and butylamine.

The hydroxy amine of group IV(c) may be a primary, secondary or tertiaryamine. It may contain one, two or three hydroxy groups. In a preferredembodiment each hydrocarbyl substituent of the nitrogen is substitutedby not more than one hydroxy group. Preferred amines have up to 20carbon atoms, more preferably between 1 and 10 and especially between 2and 4 carbon atoms as for example between 1 and 20, between 1 and 4,between 2 and 20 or between 2 and 10 carbon atoms. In secondary andtertiary amines the hydrocarbyl respectively hydroxyalkyl residues maybe the same or different. Preferred hydrocarbyl residues are alkyl, aryland alkylaryl residues, with alkyl residues being particularlypreferred. Especially preferred hydroxy amines are hydroxyalkyl amineswith 1 to 4 carbon atoms per alkyl residue. Examples for especiallypreferred hydroxy amines of group IV(c) are monoethanolamine,diethanolamine, 1-amino-2-propanol, 3-amino-1-propanol,2-amino-1-butanol, 3-amino-1-butanol, 3-amino-1-butanol,2-ethoxypropylamine, 3-ethoxypropylamine, 1-methoxyisopropylamine,2-methoxyethylamine, 2-(2-aminoethoxy)ethanol, dimethylethanolamine,N-methyldiethanolamine and monomethylethanolamine.

Preferred multifunctional amines of group IV(d) contain, besides anamino group, at least one further functional group selected from thegroup consisting of amino groups, ether groups and acid groups or anester, amide or salt thereof. Preferred multifunctional amines have upto 50 carbon atoms, more preferably between 1 and 20 and especiallybetween 2 and 10 carbon atoms as for example between 1 and 50, between 1and 10, between 2 and 50 or between 2 and 20 carbon atoms. Thehydrocarbon chains may be linear, branched and/or cyclic. In a preferredembodiment they contain 1 to 10 and especially 2 to 5 as for example 1to 5 further amino groups and/or ether groups. Preferably the amino-and/or ether groups are separated by at least two carbon atoms. Examplesfor especially preferred multifunctional amines of group IV(d) areethylenediamine, diethylenetriamine, triethylenetetramine,tetraethylenepentamine, poly(ethylene imine), propylene diamine,dipropylenetriamine, N,N-dimethyldipropylenetriamine,aminoethylenepiperazine, aminoethylethanolamine, tallow fatty propylenediamine ethoxylated with 2 to 20 moles ethylene oxide, oleyl amineethoxylated with 2 to 20 mole ethylene oxide, morpholine and piperazine.

In a further preferred embodiment the multifunctional amines of groupIV(d) contain, besides an amino group, an acid group or an ester, amideor salt thereof. Preferred acid groups are sulfonic acids, phosphoricacids and carboxylic acids. Especially preferred multifunctional aminescarrying a carboxylic acid group are amino acids. Preferred amino acidsinclude proteinogenic and non-proteinogenic amino acids. The amino groupand the carboxylic acid group may be located at the same or at differentcarbon atoms. Carboxylic acid groups and other acidic groups areespecially preferred in their neutralized form, e.g. as alkaline orearth alkaline salts. Especially preferred amino acids contain furtherfunctional groups including, hydroxyl, carboxyl, amide, ether,guanidino, hydroxyphenyl, imidazolyl and/or further amine groups.Examples of preferred multifunctional amines carrying and acid group areglycine, alanine, leucine, isoleucine, proline, serine, threonine,asparagine, glutamine, phenylalanine, tryptophan, tyrosine, valine,aspartic acid, glutamic acid, methionine, sarcosine and taurine andtheir carboxylate salts with sodium and/or potassium. Especiallypreferred amino acids are glycine, lysine, histidine and arginine.

When mixtures IV(d) of alkaline compounds of the groups IV(a) to IV(c)are used, they may comprise 2 or more, preferably 2 to 10 and especially3 to 5 as for example two, three, four or five different componentsselected form the groups IV(a) to IV(c). The portion of each individualcompound in the mixture of the compounds of groups IV(a) to IV(c) ispreferably between 5 and 95 wt.-%, more preferably between 10 and 90wt.-% and especially between 20 and 80 wt.-% as for example between 5and 90 wt.-%, between 5 and 80 wt.-%, between 10 and 95 wt.-%, between10 and 80 wt.-%, between 20 and 95 wt.-% or between 20 and 90 wt.-%.

Group V

The group V component is optional. This group comprises emulsionbreakers, demulsifiers and/or non-emulsifiers. The purpose of having thecompounds of group V present is to prevent the formation of emulsionsduring the scavenging process and to improve the efficiency of thescavenging process. Often metal sulfides as for example iron sulfide areformed e.g. by corrosion of pipelines and equipment in the presence ofsulfhydryl compounds. Being in the form of fine solids they accumulateat the oil water interface, thereby stabilizing the water present in theoil and generating a stable emulsion which may affect phase separationand accessibility of the sulfhydryl compounds to be scavenged. Thepurpose of the emulsion breaker, demulsifier and/or non-emulsifier is tobreak the oil/water emulsion by creating a preferentially water wetsurface on the metal sulfide and also to modify the surface tension atthe oil/water interface which is stabilized by the metal sulfides to oneallowing coalescence of the emulsion.

In a preferred embodiment, the emulsion breaker of group V is part ofthe inventive composition comprising compounds of groups I and II, ofgroups I, II and III, of groups I, II and IV or of groups I, II, III andIV. Preferred emulsion breakers are polymeric nonionic surfactants,including but not limited to polysorbates, polymers comprising ethyleneoxide, polymers comprising propylene oxide, ethylene oxide-propyleneoxide copolymers, alkyl polyglucosides such as decyl maltoside,alkylphenol ethoxylates, and ethoxylated and/or propoxylated alkylphenol-formaldehyde resins. The emulsion breaker can also be a fattyalcohol alkoxylated with 1 to 200 moles, preferably with 2 to 100 molesand especially with 5 to 50 moles as for example with 1 to 100 moles or1 to 50 moles or 2 to 50 moles or with 5 to 100 moles of alkylene oxide.Examples for preferred alkylene oxides are ethylene oxide, propyleneoxide and their mixtures; preferred fatty alcohols have a C₄- toC₃₆-alkyl residue and especially a C₈- to C₂₄-alkyl residue as forexample a C₄- to C₂₄-alkyl residue or a C₈- to C₃₂-alkyl residue such ascetyl alcohol and oleyl alcohol.

In a preferred embodiment, the emulsion breaker is a compound accordingto the formula (7)

wherein

R₁₀ C₂ to C₄ alkylene

R₁₁ C₁ to C₁₈ alkyl

k a number from 1 to 200

m a number from 1 to 100 is.

In a preferred embodiment R₁₀ is an ethylene or a propylene group. R₁₀may represent mixtures of different C₂ to C₄ alkylene groups, preferablyethylene and propylene groups.

In another preferred embodiment, R₁₁ is a C₄ to C₁₂ alkyl group, morepreferably a tertiary butyl group or an iso-nonyl group.

In formula (7), R₁₀, R₁₁ and k may be the same in each of the repeatingunits, or they may differ from unit to unit.

In another preferred embodiment k is a number from 2 to 20.

In another preferred embodiment m is a number from 3 to 20.

In another specific preferred embodiment the emulsion breaker is analkylbenzenesulfonic as for example dodecylbenzesulfonic acid (8) or itssalt with an alkaline metal, ammonia or a primary, secondary or tertiaryamine as for example methylamine, ethylamine, propylamine, diethylamine,dimethylamine, trimethylamine, ethanolamine, diethanolamine ortriethanolamine.

In another preferred embodiment, the demulsifier is a mixture of atleast one compound of formula (7) and an alkylbenzene sulfonic acid (8)or its salt. Such mixture preferably contains (7) and sulfonic acid (8),respectively its salt, in a weight ratio of from 5:1 to 1:5, morepreferably in a weight ratio of from 3:1 to 1:3.

The polymeric nonionic surfactant may be added to the further componentsof the inventive composition neat or preferably dissolved or suspendedin a solvent. Any solvent suitable for dissolving or suspending apolymeric nonionic surfactant may be used. Examples of suitable solventsinclude water, ethylene glycol, propylene glycol, butylene glycol,oligoethylene glycols, oligopropylene glycols, ethers including glycolethers like methoxyethane, dimethoxyethane and butoxyethanol, alcohols,toluene, xylene, aromatic naphtha, or any combination thereof. Thealcohol may include any alcohol suitable for use with oil recovery andfor dissolving the polymeric nonionic surfactant and is preferablyselected from the group consisting of methanol, ethanol, propanol,isopropyl alcohol, butanol, 2-ethyl hexanol or any combination thereof.

Group VI

The group VI component is optional. This group comprises corrosioninhibitors and serves to add corrosion inhibition functionality to theinventive composition. The addition of a corrosion inhibitor may not berequired because the synergist of group III provides sufficientcorrosion inhibition to protect the integrity of the whole asset.

However, often addition of a further corrosion inhibitor is advisable toreduce the overall corrosivity, protecting the tubulars and productionequipment from corrosion caused by oilfield fluids and gases into whichthe instant invention is deployed.

A preferred embodiment of the current invention is to use alkyl dimethylbenzyl ammonium chloride according to formula (9) as a corrosioninhibitor that also provides functionality as an interfacial tensionreducer.

wherein R⁹ is C₈ to C₁₈ alkyl.

The inventive composition may additionally contain biocides, forexample, formaldehyde or glutaraldehyde, water dispersants such aspolyacrylamide based dispersants, oxygen scavengers, antifoams such asacetylenic diols, silicones or polyethoxylated antifoams, and/orflocculants. Preferably their content is less than 10 wt.-% andespecially less than 5 wt.-% relative to the components of the groups Ito VI.

In a preferred embodiment, the inventive composition comprises 1 to 60wt.-% based on its content of active components of groups I to IV of thereaction product of the monohydric alcohol described above in group I,preferably between 5 and 50 wt.-% and especially between 10 and 40 wt.-%as for example between 1 and 50 wt.-% or between 1 and 40 wt.-% orbetween 5 and 60 wt.-% or between 5 and 40 wt.-% or between 10 and 60wt.-% or between 10 and 50 wt.-%.

In a preferred embodiment, the inventive composition comprises 1 to 95wt.-% based on its content of active components of groups I to IV of thereaction product of the sugar alcohol described above in group II,preferably between 10 and 90 wt.-%, more preferably between 20 and 80wt.-% and especially between 25 and 75 wt.-% as for example between 1and 90 wt.-% or between 1 and 80 wt.-% or 1 and 75 wt.-% or between 10and 95 wt.-% or between 10 and 80 wt.-% or between 10 and 75 wt.-% orbetween 20 and 95 wt.-% or between 20 and 90 wt.-% or between 20 and 75wt.-% or between 25 and 90 wt.-% or between 25 and 80 wt.-%.

The molar ratio between the reaction product of the monohydric alcoholand an aldehyde or ketone (group I) and the reaction product of thesugar alcohol and an aldehyde or ketone (group II) is preferably between20:1 and 1:20, preferably between 10:1 and 1:10 and especially between5:1 and 1:5 as for example between 20:1 and 1:10, between 20:1 and 1:5,between 10:1 and 1:20, between 10:1 and 1:5, between 5:1 and 1:20 orbetween 5:1 and 1:10.

In a preferred embodiment, the inventive composition comprises 0.1 to 20wt.-% based on its content of active components of groups I to IV of thesynergist described above in group III, preferably between 0.5 and 15wt.-% and especially between 1 and 10 wt.-% as for example between 0.1and 15 wt.-% or between 0.1 and 10 wt.-% or between 0.5 and 20 wt.-% orbetween 0.5 and 10 wt.-% or between 1 and 20 wt.-% or between 1 and 15wt.-%.

The weight ratio between the reaction products of group I and group IItogether and the synergist (group III) on the other hand side ispreferably between 1000:1 and 5:1, more preferably between 500:1 and10:1 and especially between 100:1 and 10:1 as for example between 1000:1and 10:1, between 500:1 and 5:1 or between 100:1 and 5:1.

In a preferred embodiment, the inventive composition comprises 0.1 to 15wt.-% based on its content of active components of groups I to IV of atleast one solids suppression agent described above in group IV,preferably between 0.5 and 10 wt.-% and especially between 1 and 8wt.-%, as for example between 1 and 10 wt.-% or between 1 and 8 wt.-% orbetween 5 and 15 wt.-% or between 5 and 8 wt.-% or between 7 and 15wt.-% or between 7 and 10 wt.-%.

In a preferred embodiment, the inventive composition comprises 0.1 to 10wt.-% based on its content of active components of groups I to VI of atleast one emulsion breaker described above in group V, preferablybetween 0.5 and 5 wt.-%.

In a preferred embodiment, the inventive composition comprises 0.1 to 10wt.-% based on its content of active components of groups I to VI of thecorrosion inhibitor described above in group VI, preferably between 0.2and 5 wt.-%.

In a preferred embodiment the compounds of groups Ito IV sum up to 100wt.-%. In a further preferred embodiment the compounds of groups I to IVsum up to 100 wt.-%.

The inventive composition is preferably applied to the oil or gas to betreated in amounts of 0.5 to 50 wt.-ppm, more preferably 1 to 30 wt.-ppmand especially 2 to 20 wt.-ppm as for example 0.5 to 3 wt.-ppm, 0.5 to20 wt.-ppm, 1 to 50 wt.-ppm, 1 to 20 wt.-ppm, 2 to 50 wt.-ppm or 2 to 30wt.-ppm per 1 ppm of sulfur contained in the oil or gas.

The use of undiluted compositions according to the invention has provenespecially successful in gas contact towers.

In a preferred embodiment the compositions according to the differentaspects of the invention are used in formulations additionallycomprising water. The water in the formulation may be formed during themanufacture of hemiacetals, or it can be introduced as a solvent for thereactants or it can be added to the composition to balance theformulation. Preferably water is present in a concentration from 1 to 90wt.-%, preferably between 5 and 80 wt.-% as for example between 1 and 80wt.-% or 5 and 90 wt.-% of the formulation. In another preferredembodiment water is present to balance up to 100 wt.-% of theformulation.

Alternatively, any balance remaining in a formulated compositionaccording to the different aspects of the invention is made up withwater and/or glycol and/or alcohol based solvents in the amounts givenabove for water alone. Preferred alcohols and glycols are selected from,but not limited to, methanol, ethanol, propan-1-ol, propan-2-ol,ethylene glycol, diethylene glycol, triethylene glycol, neopentylglycol, 2-butoxyethanol, glycerol and their mixtures.

The inventive compositions can be made by mixing of the compounds ofgroups I and II, of groups I, II and III, of groups I, II and IVrespectively of groups I, II, II and IV each optionally with compoundsof groups V and/or VI. The sequence of addition of the individualcompounds is not important. In a preferred embodiment the compounds ofgroups I and II are produced simultaneously in a single pot reaction andsubsequently the compounds of groups III and/or IV and optionally Vand/or VI are added. For the production of formulations water and/orother solvents can be added to the inventive composition. Alternatively,some or all of the components to make up the inventive composition maycontain solvent.

A formulated product containing the inventive composition and solvent ispreferably applied in concentrations between 5 and 40,000 mg/L,preferably between 50 and 30,000 mg/L and especially between 100 and25,000 mg/L as for example between 5 and 40,000 mg/L, between 5 and25,000 mg/L, between 50 and 40,000 mg/L, between 50 and 25,000 mg/L,between 100 and 40,000 mg/L and between 100 and 30,000 mg/L based on thevolume of oil or gas production to be treated. The preferred and bestsuited concentration of the formulation depends on the formulationactivity itself, the type and amount of sulfhydryl compounds to bescavenged, static conditions, temperature and salinity of the system.Furthermore, the material grade of the equipment used for operating thescavenging process should be taken into account: If e.g. a contact toweris made of stainless steel a more concentrated product can be appliedwhile it has proven to be advantageous to apply more dilute productformulations, preferably containing a corrosion inhibitor of group VI,if a poor material of construction as for example carbon steel is used.

At the given concentration range, the inventive composition providessubstantial scavenging of sulfhydryl compounds from the treated liquidsand gases and ensures a specified sulfur content of e. g. the producedhydrocarbon as it is brought to the market and therefore its safehandling. Furthermore flowability of the treated hydrocarbon will not beimpaired due to retardation resp. prevention of the formation of solidsulfhydryl reaction products.

The present invention also includes a process for application of theinventive composition in scavenging of sulfhydryl compounds present inthe drilling and the production cycle of mineral oil, particularly as acomponent of well work-over, well intervention, production enhancementand flow assurance packages.

The composition according to the invention may be injected into asulfhydryl compound containing stream together with other ingredientsknown to those familiar with the art. Such other ingredients includeacids, dispersants, viscosifiers, lubricity agents, scale inhibitors,friction reducers, cross linker, surfactants, pH adjuster, iron controlagents, breakers; this is especially advantageous if any produced water(or recycled water) is in contact with the compositions of the instantinvention.

Employing the embodiments of the instant invention allows either i) fora lower dosage rate of scavenger to obtain the same level of residualamount of sulfhydryl compound or ii) for a lower level of residualamount of sulfhydryl compound with the same dosage rate of scavenger incomparison to hemiacetals and/or acetals according to the state of theart. Additionally, in combination with a reaction product fromformaldehyde and an amine the kinetics of scavenging H₂S and/ormercaptans provided by the mixture of hemiacetals and/or acetals of amonohydric alcohol and a sugar alcohol with an aldehyde and/or ketonecan be significantly accelerated. This allows for a much more efficientscavenging of sulfhydryl compounds especially in applications where onlyshort contact times between the oil or gas and the scavenger areavailable, as for example in contact towers and direct injectionapplications for treatment of gases. By admixture of a solidssuppression agent to the mixture of hemiacetals and/or acetals of amonohydric alcohol and a sugar alcohol with an aldehyde and/or ketone asa further synergistic additive the gas breakthrough time of a systemcontaining sulfhydryl compounds is extended. While improving thescavenging of sulfhydryl compounds no formation of complex and difficultto treat emulsions is observed. Furthermore the embodiments of theinstant invention will not corrode the oilfield equipment that it comesinto contact with, nor will it allow the deposition of unwanted solids,such as polymethylenesulfide oligomers and metal sulfide scales, sooften found with applications of the prior art. Other applications ofthe embodiments of the instantaneous invention include treating waterfor downhole injection for pressure support, treatment of drilling andwork-over operations, wettability alteration and well cleanout.

Within this specification, percentages are weight percentages unlessspecified otherwise.

EXAMPLES

Preparation of Hemiacetals

Method A (using paraformaldehyde, PFA): The amounts of alcohol and watergiven in table 1 were charged into a stirred reactor. 0.25 wt.-% (basedon the mass of alcohols) of sodium hydroxide solution at 50 wt.-% wasadded. This mixture was homogenized for 10 minutes beforeparaformaldehyde (PFA, 93 wt.-%) was added in the amount given in table1 over a period of approximately 30 minutes. The reaction mixture waswarmed while stirring for 8 hours at a temperature between 80 to 85° C.After the reaction time, the mixture was cooled to 30° C.

Method B (using aqueous formaldehyde, AFA): A stirred reactor wascharged with the quantities of an aqueous solution of formaldehyde (AFA,37 wt.-%) given in table 1 . Then, amounts of alcohols given in table 1were added followed by 0.25 wt.-% (based on the mass of alcohols) ofsodium hydroxide solution at 50 wt.-%. This mixture was homogenized for10 minutes before heating the stirred reaction mixture to a temperaturebetween 80 to 85° C. for 8 hours. After the reaction time, the mixturewas cooled to 30° C.

The sugars were used as pure reagents; in examples A5, A11, A13 and A14sorbitol was used as a 70 wt.-% active aqueous solution.

The reaction products are characterized by the molar amounts ofhemiacetal in respect to the total amount of hydroxyl groups charged andthe content of free formaldehyde (CH₂O) as determined by ¹H NMRspectroscopy.

Further materials used were

-   -   hexahydro-1,3,5-trimethyl-s-triazin (HTT) and        3,3′-methylenebis-5-methyloxazolidine (MBO) as the synergists        according to group III.    -   triethylamine (TEA), monoethanolamine (MEA), piperazine (PIP), 5        wt.-% aqueous solution of NaOH (NaOH), and the monosodium salt        of glycine (GLY) as the solids suppressants according to        group IV. All these materials were commercial grades.

TABLE 1 Preparation of (hemi-)acetals reactor charge formaldehydereaction product monohydric charge sugar charge water source; chargeacetalized free CH₂O (hemi-)acetal alcohol [g] alcohol [g] [g] [g][mol-%] [wt.-%] A1 (comp.) methanol 500 — 0 0 PFA 500 98% 0.07 A2(comp.) ethanol 600 — 0 0 PFA 420 99% 0.06 A3 (comp.) i-propanol 600 — 00 PFA 320 99% 0.08 A4 (comp.) 2-EH 800 — 0 0 PFA 200 98% 0.11 A5 (comp.)— 0 sorbitol (aq.) 692 0 AFA 1208 79% 0.07 A6 (comp.) — 0 xylitol 490 0AFA 1046 77% 0.09 A7 (comp.) — 0 isomalt 1416 1513 PFA 955 65% 0.13 A8(comp.) — 0 inositol 931 400 PFA 800 75% 0.08 A9 (comp.) — 0 mannitol212 0 AFA 368 64% 0.09 A10 (comp.) — 0 erythritol 155 178 PFA 113 69%0.05 A11 ethanol 23 sorbitol (aq.) 130 0 AFA 227 76% 0.07 A12 methanol19 sorbitol 108 46 AFA 270 78% 0.06 A13 methanol 19 sorbitol (aq.) 154170 PFA 107 78% 0.08 A14 methanol 19 sorbitol (aq.) 154 0 AFA 337 97%0.05 A15 methanol 80 xylitol 380 143 PFA 387 77% 0.07 A16 methanol 45isomalt 484 575 PFA 363 68% 0.14 A17 methanol 75 inositol 422 670 PFA423 76% 0.08 A18 methanol 77 mannitol 438 688 PFA 434 77% 0.08 A19methanol 86 erythritol 328 0 AFA 654 59% 0.10 A20 i-propanol 150erythritol 305 0 AFA 608 56% 0.14 2-EH = 2-ethyl hexanol; (aq.) =aqueous solution, 70% active

Scavenger Performance Tests—Efficiency

In order to demonstrate the improved efficiency of the instant inventionin removing sulfhydryl compounds compared to group I respectively groupII compounds alone, the removal of H₂S from an oil and from an oil/watermixture was measured.

The oil used was a mixture of kerosene with 10% of xylene with zerobottom sediment and water (BS&W) to simulate oil field conditions.

The oil/water mixture was a mixture of the oil described above and brine(in a 50:50 volume ratio of oil to aqueous phase) to mimic theefficiency in hydrated crude oil.

In a 500 mL stirred autoclave (Parr reactor), 350 mL of the oilrespectively the oil/brine mixture was de-aerated for 1 hour with N₂,then saturated with a sour gas mixture of 0.2 wt.-% H₂S and 99.8 wt.-%CO₂, by purging this gas into the oil resp. oil/brine mixture with aflow rate of 0.6 L/min. After equilibration by the sour gas mixture,1.000 ppm of the composition to be tested was injected into theautoclave by an HPLC pump.

For reasons of better comparability of performance tests thecompositions given in tables 2 and 3 containing (hemi-)acetal, synergistand/or solids suppressant as active materials, were applied as 50 wt.-%active formulations in water. The portions of (hemi-)acetal, synergistand solids suppressant given in tables 2, 3 and 4 refer to the portionof the respective component in the active material, therefore summing upto 100%. For preparation of the compositions given in tables 2, 3 and 4the water content introduced during preparation of the (hemi-)acetals A1to A20 according to table 1 was taken into account.

The performance tests were carried out at 30° C. and under 1 bar, usinga gas chromatograph to measure the outlet H₂S content in the gas phaseevery two minutes. Then, a graph of the measured values of H₂S content(ppm) versus time (min) was plotted. The amount of hydrogen sulfidescavenged is the area above the resultant performance curve, which iscalculated by the integration of the curve. For all samples theintegration of the curve was done up to 60 min after the injection ofH₂S-scavenger. As the output parameter of this performance testL_(sc)/kgH₂S (Liters of H₂S scavenger required to remove 1 kg of H₂Sfrom the system) has been determined for 6 minutes and 1 hour ofanalysis. All consumption values (L_(sc)/kgH₂S) refer to the amount of100% active composition consumed in the test and are averages of threerepeat tests. The test results have been summarized in Table 2 and Table3. Percentages mean weight percent if not indicated otherwise. Ratios inmixtures of (hemi-)acetals refer to mass portions of active material.

TABLE 2 Performance tests for H₂S-scavengers in oil (zero BS&W) solids(hemi)acetal synergist suppressant amount amount amount L_(SC)/kg H₂Sexample Type [wt %] Type [wt %] Type [wt %] @ 6 min. @ 1 hour P1 (comp.)A1 100 — 0 — 0 19.45 8.70 P2 (comp.) A2 100 — 0 — 0 20.76 9.56 P3(comp.) A3 100 — 0 — 0 21.23 10.04 P4 (comp.) A5 100 — 0 — 0 19.62 9.23P5 (comp.) A6 100 — 0 — 0 18.57 8.58 P6 (comp.) A7 100 — 0 — 0 20.0810.35 P7 (comp.) A1 + A2 (1:1) 100 — 0 — 0 19.12 9.85 P8 (comp.) A5 + A6(2:1) 100 — 0 — 0 17.68 9.05 P9 A1 + A5 (1:4) 100 — 0 — 0 14.56 7.45 P10A2 + A5 (1:1) 100 — 0 — 0 14.77 7.53 P11 A3 + A6 (1:3) 100 — 0 — 0 14.067.43 P12 A3 + A7 (2:1) 100 — 0 — 0 14.78 7.72 P13 A11 100 — 0 — 0 12.226.43 P14 A12 100 — 0 — 0 12.05 6.32 P15 A15 100 — 0 — 0 12.43 6.71 P16A1 + A5 (1:4) 93 — 0 MEA 7 11.79 6.06 P17 A2 + A5 (1:1) 93 — 0 GLY 711.65 5.99 P18 A3 + A7 (2:1) 95 — 0 NaOH 5 11.81 6.02 P19 A11 93 — 0 GLY7 11.88 5.98 P20 A12 93 — 0 MEA 7 11.79 6.03 P21 A15 93 — 0 GLY 7 11.656.20 P22 A16 93 — 0 PIP 7 11.81 6.32 P23 (comp.) A1 98 MBO 2 — 0 6.224.73 P24 (comp.) A2 98 MBO 2 — 0 6.65 4.87 P25 (comp.) A5 98 MBO 2 — 05.32 4.43 P26 (comp.) A6 98 MBO 2 — 0 5.21 4.64 P27 A1 + A5 (1:4) 98 MBO2 — 0 3.21 2.68 P28 A2 + A5 (1:1) 98 MBO 2 — 0 3.12 2.75 P29 A3 + A6(1:3) 98 MBO 2 — 0 3.43 2.97 P30 A11 98 MBO 2 — 0 2.99 2.65 P31 A12 98MBO 2 — 0 3.05 2.62 P32 A3 + A6 (1:3) 98 MBO 2 — 0 3.55 2.81 P33 A11 96HTT 4 — 0 3.23 2.76 P34 A15 96 HTT 4 — 0 3.73 2.92 P35 A16 96 HTT 4 — 03.48 2.91 P36 (comp.) A1 93 MBO 2 MEA 5 4.85 4.13 P37 (comp.) A2 90 MBO2 PIP 8 4.94 4.20 P38 (comp.) A3 88 MBO 2 TEA 10 8.02 6.78 P39 (comp.)A5 93 MBO 2 MEA 5 4.68 3.23 P40 (comp.) A6 90 MBO 2 GLY 8 4.75 3.26 P41A1 + A5 (1:4) 93 MBO 2 MEA 5 2.25 1.99 P42 A2 + A5 (1:1) 93 MBO 2 MEA 52.41 2.07 P43 A3 + A7 (1:3) 88 MBO 2 TEA 10 2.60 2.31 P44 A11 93 MBO 2MEA 5 2.20 1.87 P45 A12 93 MBO 2 MEA 5 2.13 1.85 P46 A3 + A6 (1:3) 90MBO 2 PIP 8 2.55 2.28 P47 A12 89 HTT 4 GLY 7 2.15 1.84 P49 A13 89 HTT 4GLY 7 2.43 1.90 P50 A13 89 HTT 4 MEA 7 2.47 1.92 P51 A15 89 HTT 4 GLY 72.36 1.83 P52 A15 89 HTT 4 MEA 7 2.34 1.85 P53 A16 89 HTT 4 GLY 7 2.401.89

TABLE 3 Performance tests for H₂S-scavenging in a mixture of the oil andbrine (50:50 volume ratio of oil to aqueous phase) solids (hemi)acetalsynergist suppressant amount amount amount L_(SC)/kg H₂S example type[wt %] type [wt %] type [wt %] @ 6 min. @ 1 hour P54 (comp.) A1 100 — 0— 0 23.36 10.04 P55 (comp.) A2 100 — 0 — 0 23.82 10.20 P56 (comp.) A4100 — 0 — 0 23.60 12.20 P57 (comp.) A5 100 — 0 — 0 22.78 9.31 P58(comp.) A8 100 — 0 — 0 22.27 10.08 P59 (comp.) A9 100 — 0 — 0 23.0710.32 P60 (comp.) A10 100 — 0 — 0 22.97 10.27 P61 (comp.) A1 + A2 (1:1)100 — 0 — 0 21.87 9.95 P62 (comp.) A5 + A9 (2:1) 100 — 0 — 0 20.34 9.55P63 A1 + A5 (1:4) 100 — 0 — 0 15.93 7.78 P64 A2 + A5 (1:1) 100 — 0 — 014.97 7.83 P65 A1 + A9 (1:3) 100 — 0 — 0 15.36 8.36 P67 A13 100 — 0 — 013.42 7.63 P68 A14 100 — 0 — 0 13.52 7.72 P69 A17 100 — 0 — 0 13.57 7.74P70 A19 100 — 0 — 0 13.31 7.51 P71 A1 + A5 (1:4) 93 — 0 GLY 7 12.95 7.03P72 A1 + A9 (1:3) 93 — 0 PIP 7 13.47 7.26 P73 A13 93 — 0 GLY 7 13.687.48 P74 A13 93 — 0 MEA 7 13.37 7.97 P75 A14 93 — 0 GLY 7 14.03 7.48 P76A14 93 — 0 MEA 7 14.56 7.44 P77 A17 93 — 0 GLY 7 15.00 7.40 P78 A19 93 —0 NaOH 5 14.81 7.62 P79 (comp.) A1 98 MBO 2 — 0 8.29 6.63 P80 (comp.) A298 MBO 2 — 0 8.40 6.88 P81 (comp.) A4 98 MBO 2 — 0 9.84 6.55 P82 (comp.)A5 98 MBO 2 — 0 8.56 6.80 P83 (comp.) A9 98 MBO 2 — 0 8.26 6.65 P84 A1 +A5 (1:4) 98 MBO 2 — 0 6.29 5.03 P85 A2 + A5 (1:1) 98 MBO 2 — 0 6.12 4.99P86 A1 + A10 (1:3) 98 MBO 2 — 0 6.43 5.17 P87 A13 98 MBO 2 — 0 6.05 5.12P88 A14 98 MBO 2 — 0 6.12 5.20 P89 A4 + A9 (1:3) 98 MBO 2 — 0 6.55 5.81P90 A13 96 HTT 4 — 0 6.44 5.76 P91 A14 96 HTT 4 — 0 7.03 5.92 P92 A18 96HTT 4 — 0 6.54 5.84 P93 (comp.) A1 88 MBO 2 MEA 10 6.52 5.56 P94 (comp.)A2 90 MBO 2 PIP 8 6.94 5.71 P95 (comp.) A4 88 MBO 2 TEA 10 6.75 5.49 P96(comp.) A5 88 MBO 2 MEA 10 7.05 5.92 P97 (comp.) A10 90 MBO 2 PIP 8 6.755.57 P98 A1 + A5 (1:4) 93 MBO 2 MEA 5 4.25 3.82 P99 A2 + A5 (1:1) 93 MBO2 MEA 5 4.31 3.90 P100 A4 + A19 (1:3) 88 MBO 2 TEA 10 4.60 4.01 P101 A1393 MBO 2 MEA 5 4.24 3.80 P102 A14 93 MBO 2 MEA 5 4.27 3.85 P103 A4 + A9(1:3) 90 MBO 2 PIP 8 4.85 3.94 P104 A10 89 HTT 4 GLY 7 4.15 3.75 P105A13 89 HTT 4 GLY 7 4.53 3.89 P106 A13 91 HTT 4 NaOH 5 4.49 3.84 P107 A1489 HTT 4 GLY 7 4.81 4.01 P108 A14 89 HTT 4 MEA 7 4.63 4.05 P109 A18 89HTT 4 GLY 7 4.41 5.84 P110 A18 89 HTT 4 MEA 7 4.43 4.83 P111 A19 89 HTT4 GLY 7 4.61 3.89 P112 A20 89 HTT 4 PIP 7 4.76 3.99

In tables 2 and 3 the lower consumption of the scavenger to remove 1 kgof H₂S, the more efficient is the scavenger. In the inventive examplesthe mixtures of acetals being based on mixtures of monohydric alcoholsand sugar alcohols are more efficient than the single components. Theefficiency is further improved by the incorporation of a synergistand/or a solids suppressant. Furthermore, incorporation of the synergistenhances the reaction rate in the initial phase of the test as can beseen from the difference between scavenging efficiency after 6 minutesversus 1 hour.

Scavenger Performance Tests—Gas Breakthrough

The performance of the H₂S scavengers according to the invention wasevaluated for their ability to remove H₂S from a flowing gas stream bypassing gas laden with H₂S through a column of fluid containing thescavenger chemical. A sour gas mixture of 0.2% H₂S and 99.8% CO₂ ispurged with a flow rate of 60 mL/min through 440 mL of a 22% activesolution of the scavenger composition in water. Under these conditionsthe average contact time of gas and scavenger was about 4 seconds.Initially all of the H₂S is removed from the gas stream and no H₂S isdetected in the effluent gas. At some point in time (the breakthroughtime or TBT) the chemical can no longer entirely remove H₂S from the gasstream and H₂S is observed in the effluent. This parameter is a measureof the efficacy of the scavenger especially for contact towerapplications with short contact time. The longer the break through timethe more efficient is the chemical scavenger.

The effect of the solids suppression agent is rated by visual inspectionof the spent scavenger fluid after the gas breakthrough test. The degreeof solids formation is rated opaque>turbid>opalescent>clear.

The overall concentration of the scavenger formulations in all examplesis 22 wt.-% (active ingredients), i. e. in examples where synergistand/or solids suppressant is present the concentration of (hemi-)acetalsis reduced accordingly.

TABLE 4 Gas breakthrough times for different (hemi-)acetals solids(hemi-)acetal synergist suppressant amount amount amount TBT visualexample type [wt.-%] type [wt-%] type [wt-%] [min] inspection B1 (comp.)A1 100 — 0 — 0 31 opaque B2 (comp.) A2 100 — 0 — 0 29 opaque B3 (comp.)A5 100 — 0 — 0 19 opaque B4 (comp.) A7 100 — 0 — 0 29 opaque B5 (comp.)A10 100 — 0 — 0 54 opaque B6 (comp.) A1 + A2 (1:1) 100 — 0 — 0 31 opaqueB7 (comp.) A5 + A7 (1:1) 100 — 0 — 0 35 opaque B8 A1 + A5 (1:1) 100 — 0— 0 43 opaque B9 A1 + A5 (1:4) 100 — 0 — 0 46 opaque B10 A1 + A7 (1:4)100 — 0 — 0 55 opaque B11 A2 + A10 (1:2) 100 — 0 — 0 49 opaque B12 A11100 — 0 — 0 57 opaque B13 A12 100 — 0 — 0 56 opaque B14 A18 100 — 0 — 053 opaque B15 (comp.) A1 93 MBO 7 — 0 76 turbid B16 (comp.) A2 97 HTT 3— 0 69 turbid B17 (comp.) A5 97 HTT 3 — 0 77 turbid B18 (comp.) A7 93MBO 7 — 0 75 turbid B19 A1 + A5 (1:1) 97 HTT 3 — 0 85 turbid B20 A1 + A5(1:4) 97 HTT 3 — 0 90 turbid B21 A11 97 HTT 3 — 0 88 turbid B22 A12 97HTT 3 — 0 89 turbid B23 A13 93 MBO 7 — 0 88 turbid B24 A1 + A7 (1:4) 95MBO 5 — 0 84 turbid B25 A2 + A10 (1:2) 95 HTT 5 — 0 83 turbid B26 A13 96HTT 4 — 0 85 turbid B27 A14 96 HTT 4 — 0 87 turbid B28 A16 96 HTT 4 — 084 turbid B29 (comp.) A1 90 — 0 MEA 10 149 opalescent B30 (comp.) A2 85— 0 PIP 15 146 opalescent B31 (comp.) A3 85 — 0 PIP 15 134 opalescentB32 (comp.) A5 85 — 0 PIP 15 153 opalescent B33 (comp.) A7 90 — 0 MEA 10147 opalescent B34 A1 + A5 (1:1) 85 — 0 PIP 15 167 opalescent B35 A1 +A5 (1:4) 85 — 0 PIP 15 180 opalescent B36 A11 85 — 0 PIP 15 166opalescent B37 A12 85 — 0 PIP 15 177 opalescent B38 A13 95 — 0 NaOH 5167 opalescent B39 A13 93 — 0 MEA 7 165 opalescent B40 A14 93 — 0 GLY 7158 opalescent B41 A14 93 — 0 MEA 7 159 opalescent B42 A16 90 — 0 MEA 10172 opalescent B43 A1 + A7 (1:4) 85 — 0 PIP 15 170 opalescent B44 A2 +A7 (1:2) 85 — 0 PIP 15 161 opalescent B45 A19 93 — 0 GLY 7 169opalescent B46 (comp.) A1 83 MBO 7 MEA 10 215 clear B47 (comp.) A2 82HTT 3 PIP 15 200 clear B48 (comp.) A3 90 HTT 5 PIP 15 192 clear B49(comp.) A5 82 HTT 3 PIP 15 221 clear B50 (comp.) A7 83 MBO 7 MEA 10 219clear B51 A1 + A5 (1:1) 82 HTT 3 PIP 15 258 clear B52 A1 + A5 (1:4) 82HTT 3 PIP 15 288 clear B53 A11 82 HTT 3 PIP 15 305 clear B54 A12 82 HTT3 PIP 15 310 clear B55 A12 83 MBO 7 MEA 10 300 clear B56 A1 + A7 (1:4)80 MBO 5 PIP 15 299 clear B57 A2 + A10 (1:2) 80 HTT 5 PIP 15 295 clearB58 A10 89 HTT 4 GLY 7 320 clear B59 A13 89 HTT 4 GLY 7 311 clear B60A13 89 HTT 4 MEA 7 309 clear B61 A14 89 HTT 4 GLY 7 295 clear B62 A14 91HTT 4 NaOH 5 297 clear B63 A19 89 HTT 4 MEA 7 298 clear

A comparison of the inventive examples and the comparative examplesshows that mixtures of (hemi-)acetals containing reaction products ofmonohydric and sugar alcohols have a higher TBT than the singlecomponents or mixtures of components of the same group. The addition ofa synergist according to group III increases the H₂S scavenging activityof (hemi-)acetals and especially of mixtures of (hemi-)acetalssignificantly. The scavenging process becomes faster and more efficient.The addition of a solids suppressant further significantly improves theperformance of the scavenger. Formation of solids is mostly inhibitedwhich otherwise hampers the accessibility of part of the scavenger andfurthermore bears the risk of clogging flow lines for the effluent. Theenhancement in scavenging efficiency exceeds the stoichiometric H₂Sscavenging capacity of the added synergist considerably.

1. Composition comprising I. at least one reaction product between anitrogen-free monohydric alcohol and an aldehyde or ketone, and II. atleast one reaction product between a sugar alcohol and an aldehyde orketone.
 2. Composition according to claim 1, further comprising III. atleast one reaction product from formaldehyde and ammonia and/or anamine, selected from the group consisting of primary alkyl amines having1 to 10 carbon atoms, and primary hydroxy alkyl amines having 2 to 10carbon atoms.
 3. Composition according to claim 1, further comprisingIV. at least one inorganic or organic alkaline compound that functionsas a solids suppression agent.
 4. Composition according to claim 1,wherein the reaction products I. and II. are hemiacetals and/or acetals.5. The composition according to claim 1, wherein the aldehyde or ketonecontains 1 to 10 carbon atoms, preferably 1 to 4 carbon atoms.
 6. Thecomposition according to claim 1, wherein the aldehyde or ketone isselected from the group consisting of formaldehyde, paraformaldehyde,glyoxal, acetaldehyde, propionaldehyde, butyraldehyde andglutaraldehyde.
 7. The composition according to claim 1, wherein thealdehyde or ketone is formaldehyde.
 8. The composition according toclaim 1, wherein the monohydric alcohol comprises 1 to 15 carbon atoms,preferably 1 to 5 carbon atoms.
 9. The composition according to claim 1,wherein the monohydric alcohol is an aliphatic alcohol.
 10. Thecomposition according to claim 1, wherein the monohydric alcohol isselected from the group consisting of methanol, ethanol, propanol,iso-propanol, n-butanol, iso-butanol, tert-butanol, pentanol, hexanol,heptanol and octanol, and any mixture thereof.
 11. The compositionaccording to claim 1, wherein the sugar alcohol is a polyol obtainableby reduction of a sugar.
 12. The composition according to claim 1,wherein the sugar alcohol contains 4 to 12 carbon atoms and 4 to 10hydroxy groups wherein not more than one hydroxy group is attached toeach carbon atom.
 13. The composition according to claim 1, wherein thesugar alcohol is selected from tetritols, pentitols and hexitols. 14.The composition according to claim 1, wherein the sugar alcohol isselected from the group consisting of erythritol, threitol, arabitol,ribitol, xylitol, allitol, dulcitol, sorbitol, iditol, mannitol,talitol, inositol.
 15. The composition according to claim 1, wherein thesugar alcohol is a linear sugar alcohol having the general formula (1)HO—CH₂—(CHOH)_(n)—CH₂—OH   (1) wherein n is 2, 3 or
 4. 16. Thecomposition according to claim 1, wherein the reaction product between asugar alcohol and an aldehyde or ketone is selected from the groupconsisting of the compounds according to formulae (2) to (5)OHCHR₁—O—CH₂—CH(OCHR₁OH)—CH(OCHR₁OH)—CH(OCHR₁OH)—CH(OCHR₁OH)—CH₂—O—CHR₁OH  (2)OHCHR₁—O—CH₂—CH(OCHR₁OH)—CHOH—CH(OCHR₁OH)—CH(OCHR₁OH)—CH₂—O—CHR₁OH   (3)OHCHR₁—O—CH₂—CH(OCHR₁OH)—CHOH—CH(OCHR₁OH)—CHOH—CH₂—O—CHR₁OH   (4)OH—CH₂—CH(OCHR₁OH)—CHOH—CH(OCHR₁OH)—CHOH—CH₂—O—CHR₁OH   (5) wherein R₁is H or C₁ to C₉ alkyl
 17. The composition according to claim 1, whereinthe reaction product III of an amine and formaldehyde corresponds toformula (6a)

wherein R is H or methyl, and n is 1 or
 2. 18. The composition accordingto claim 1, wherein the reaction product III of an amine andformaldehyde corresponds to the formula (6b)

wherein each R² is C₁ to C₄ alkyl or C₂ to C₄ hydroxy alkyl.
 19. Thecomposition according to claim 17, wherein the compound of formula 6a is3,3′-methylenebis-5-methyl-oxazolidine.
 20. The composition according toclaim 1, wherein the reaction product III of an amine and formaldehydeis present in the composition in an amount from 1 wt.-% to 20 wt.-%,preferably between 5 wt.-% and 15 wt.-%.
 21. Composition according toclaim 3, wherein the alkaline compound IV. is selected from the groupconsisting of IV(a). alkaline metal salts or alkaline earth metal saltsIV(b). ammonia; alkyl amines, aryl amines or alkylaryl amines IV(c).hydroxy alkyl amines, hydroxy aryl amines or hydroxy alkylaryl aminesIV(d). multifunctional amines containing besides an amino group, atleast one further functional group selected from the group consisting ofamino groups, ether groups and acid groups or an ester, amide or saltthereof IV(e). mixtures of compounds of groups IV(a) to IV(c), wherein“alkyl” means C₁ to C₂₀ alkyl, “aryl” means C₆ to C₂₀ aryl and“alkylaryl” means C₇ to C₂₀ alkylaryl.
 22. Composition according toclaim 1, comprising 1 to 60 wt.-% of the reaction product between amonohydric alcohol and an aldehyde or ketone, preferably between 5 and50 wt.-%.
 23. Composition according to claim 1, comprising 1 to 95 wt.-%of the reaction product between a sugar alcohol and an aldehyde orketone, preferably between 20 and 75 wt.-%.
 24. Composition according toclaim 1, wherein the molar ratio between the reaction product between amonohydric alcohol and an aldehyde or ketone (group I) and the reactionproduct between a sugar alcohol and an aldehyde or ketone (group II) isbetween 20:1 and 1:20, more preferably 5:1 to 1:5.
 25. Compositionaccording to claim 1, wherein the ratio between the combined reactionproducts of groups I and group II on the one hand side and the synergist(group III) on the other hand side is between 1000:1 and 5:1. 26.Composition according to claim 1, comprising 0.1 to 15 wt.-%, preferably0.5 to 10 wt.-% of at least one solids suppression agent (group IV). 27.The composition according to claim 1, further comprising an alkyldimethyl benzyl ammonium chloride according to formula (9) as acorrosion inhibitor

wherein R⁹ is C₈ to C₁₈ alkyl.
 28. The composition according to claim27, wherein the compound of formula (9) is present in an amount between0.01 and 5 wt.-%, preferably between 0.5 and 2 wt.-%.
 29. Thecomposition according to claim 1, further comprising a demulsifier in anamount between 0.1 to 10 wt.-%, preferably between 0.5 and 2 wt.-%. 30.The composition according to claim 29, wherein the demulsifier isselected from the group consisting of polysorbates, fatty alcohols,polymers comprising ethylene oxide, polymers comprising propylene oxide,ethylene oxide-propylene oxide copolymers, alkyl polyglucosides,alkylphenol ethoxylates, alkyl polyethylene oxide, alkylbenzenesulfonicacid and ethoxylated and/or propoxylated alkyl phenol-formaldehyderesins.
 31. The composition according to claim 29, wherein thedemulsifier corresponds to the formula (7)

wherein R₁₀ is C₂ to C₄ alkylene, R₁₁ is C₁ to C₁₈ alkyl, k is a numberfrom 1 to 200, m is a number from 1 to
 100. 32. Composition according toclaim 29, wherein the demulsifier is dodecylbenezesulfonic acid (8)


33. Composition according to claim 29, wherein the demulsifier is amixture of at least one compound of formula (7) and at least onecompound of formula (8) in a weight ratio of from 5:1 to 1:5, preferablyin a weight ratio of from 3:1 to 1:3.
 34. Formulation, comprising 10 to99 wt.-% of a composition according to claim 1, and 1 to 90 wt.-% of asolvent selected from the group consisting of water, methanol, ethanol,propan-1-ol, propan-2-ol, ethylene glycol, diethylene glycol,triethylene glycol, neopentyl glycol, 2-butoxyethanol, glycerol andtheir mixtures, most preferably water.
 35. Use of a composition orformulation according to claim 1, for scavenging hydrogen sulphideand/or mercaptans.
 36. Use of a composition according to claim 35,wherein the scavenging occurs from fluids or gases produced fromsubterranean formations.
 37. Use according to claim 35, wherein thescavenging from gas is conducted in a contact tower or by directinjection into the gas.
 38. Process for the scavenging of hydrogensulphide and/or mercaptans, comprising adding to a medium comprisingsuch hydrogen sulphide or mercaptans a composition or formulationaccording to claim
 1. 39. Use of a reaction product from formaldehyde,and ammonia and/or an amine, selected from the group consisting ofprimary alkyl amines having 1 to 10 carbon atoms, and primary hydroxyalkyl amines having 2 to 10 carbon atoms, as a synergist in the reactionbetween between hydrogen sulphide and/or mercaptans and a compositioncomprising I. at least one reaction product between a nitrogen-freemonohydric alcohol and an aldehyde or ketone, and II. at least onereaction product between a sugar alcohol and an aldehyde or ketone. 40.Use of alkaline compound selected from the group consisting of IV(a).alkaline metal salts or alkaline earth metal salts IV(b). ammonia; alkylamines, aryl amines or alkylaryl amines IV(c). hydroxy alkyl amines,hydroxy aryl amines or hydroxy alkylaryl amines IV(d). multifunctionalamines containing besides an amino group, at least one furtherfunctional group selected from the group consisting of amino groups,ether groups and acid groups or an ester, amide or salt thereof IV(e).mixtures of compounds of groups IV(a) to IV(c). as a synergist in thereaction between between hydrogen sulphide and/or mercaptans and acomposition comprising I. at least one reaction product between anitrogen-free monohydric alcohol and an aldehyde or ketone, and II. atleast one reaction product between a sugar alcohol and an aldehyde orketone.